Percutaneous transluminal coronary angioplasty (PTCA) is a therapeutic medical procedure used to increase blood flow through the coronary artery and can often be used as an alternative to coronary by-pass surgery. An elongated catheter having a deflated balloon at its distal end is guided through a patient's cardiovascular system to the coronary artery of the heart. The balloon is inflated to compress deposits that have accumulated along the inner walls of the coronary artery to widen the artery lumen and increase blood flow. Typically, the balloon catheter is guided to the specific area within the vessel by an elongated guidewire. The guidewire is inserted into the patient and routed through the cardiovascular system and can be viewed on an x-ray imaging screen.
The path the guidewire follows during this procedure is often tortuous. The distal tip of the guidewire is flexible to avoid damaging inner walls of the blood vessels that the guidewire tip contacts along the tortuous path. The distal tip is often pre-bent to a desired configuration so that the guidewire can be inserted into branching blood vessels along its path. When the tip is pre-bent, the physician must be able to orient the tip so it can be pushed into these branching blood vessels. Examples of prior art guidewires are shown in U.S. Pat. No. 4,846,186 issued to Box et al. on Jul. 11, 1989 and U.S. Pat. No. 5,267,574 issued to Viera et al. on Dec. 7, 1993, both of which are hereby incorporated herein by reference.
Such guidewires typically have a core made from stainless steel or the like and coated with a lubricity enhancing agent, such as Teflon.RTM.. The distal end of the guidewire is not coated as such and usually comprises one or two tapered portions which reduce the diameter of the core wire at its distal end. The distal most portion of the core wire is then flattened to form a ribbon tip which makes it easier for a physician to form into a desired shape. A flexible coiled wire spring surrounds the distal tip of the core wire and is attached thereto. The coil separates from the core wire for a predetermined length and is attached proximal to the flattened distal portion of the core wire.
Other types of guidewires have cores which are made from superelastic alloys such as Nitinol.RTM.. An example of such a wire is given in U.S. Pat. No. 5,411,476 issued to Abrams et al. on May 2, 1995, which is hereby incorporated herein by reference. The superelastic nature of the core wire allows the metal to be deformed, as is typically the case as the guidewire travels through tortuous vessels, and restrained in the deformed condition, causing the alloy to transform from an austenite phase to a martensite phase. However, once the restraint on the superelastic member is removed, the stress is reduced and the core returns to its original undeformed shape by the transformation back to the original phase.
When the physician is navigating the tortuous paths of the human vasculature, it is often desirable to have the distal tip of the guidewire bent to a particular shape. This aids the guidewire in making turns into branching vessels or the like. However, during the same procedure, the physician may often want the distal tip of the guidewire to be flexible, not having a pre-bent configuration. This needs to be accomplished without removing the guidewire from the patient. Therefore, there has been a desire to have a guidewire whose tip shape can change without being removed from the body of a patient. The present invention fulfills such a desire.